1. Field of the Invention
The present invention relates to a portable information terminal powered by a secondary battery, such as a portable telephone set, a PHS (Personal Handy-phone System) terminal, a PDA (Personal Digital Assistant--portable information communication terminal), a portable game machine, etc., a battery charging device for charging the secondary battery of such a portable information terminal, and a reception system and a transmission and reception system which employ the portable information terminal and the battery charging device.
2. Description of the Related Art
Various proposals have been made in order for a portable information terminal to transmit data to and receive data from an external circuit. According to a first attempt, the portable information terminal may have a built-in data transmission and reception circuit. According to a second scheme, the portable information terminal may be connected to a data transmission and reception device via a connection cable.
However, the first proposal is disadvantageous in that the portable information terminal has a relatively large volume and weight because the area of a printed wiring board which supports the data transmission and reception circuit is increased and the portable information terminal needs to accommodate circuit components of the data transmission and reception circuit, the portable information terminal has an increased power requirement, and the portability of the portable information terminal is impaired.
The second approach is able to overcome the shortcomings of the first proposal, but is problematic in that the data transmission and reception device needs to be provided as an individual device, and the process of connecting and disconnecting the connection cable is tedious and time-consuming.
The inventor of the present invention has noticed that many portable information terminals are powered by a secondary battery in view of its convenience, and such portable information terminals are normally used in such a mode that they are carried and used by the users in daytime, and connected to a battery charger to charge the secondary battery at night.